Method of controlling the operation of a blast furnace



Feb. 14, 1967 Q H MCCLESKEY 3,304,171

METHOD oF CONTROLLING THE OPERATION 0F A BLAST FURNAGE Filed June 26, 1963 2 Sheets-Sheet l kunnen Messun- @stangen TEN/ERA TUNE NOIST'URE RELURER /NVE/VTR GEORGE H. McCLESKEY Feb. 14, 1967 H, MCCLESKEY 3,304,171

METHOD OF CONTROLLING THE OPERATION OF A BLAST FURNACE Filed June 26, 1963 2 Sheets-Sheet 2 52 Fl-; Z-

COLUMN coLUMN COLUMN coLUMN coLuMN coLuMN 8UsT1 E w1N0 ACTUAL ACTUAL ToP TEM1 ToP TEMP.

MOISTURE voLUME ausTLE 10P WIND v01.. MOISTURE coRREcT coRREcT PRESSURE TEMP. coRREcT connEcT 46\ -0.51 4f +125 25.5 580 +120 -0.2 V//EV 15,000 j] 24.0 7A 510 000 V 0.0 7/

21.0 50.0 48o /NvE/vron.

GEO/'PGE H. MCCLESKEY 21.5` 50.5 44 MM2@ 54/ 42, 51.0

Alforney United States This invention relates to a method of controlling the operation of a blast furnace and particularly an iron producing blast furnace. The operation of a blast furnace is complex and many methods have been suggested and used for controlling its operation. For example, it has been suggested to control the air or wind to the individual tuyeres. Other methods are based upon maintaining a pre-set top pressure. Still another method depends upon a drop of pressure across the burden of the furnace. However, none of these methods have proved entirely satisfactory, probably because they do not take into account the majority of all of the variables which contribute to the operation of the blast furnace. There are many such variables which include the type of burden, particularly the chemical composition and physical quality of the coke and the iron containing constituents, the blast pressure, the wind rate, the blast temperature, the amount of moisture, the top pressure, the distribution of air, and the quality and quantity of the iron to be produced. The operator has little or no control over many of these variables. For example, management will tell the operator that the iron must have low sulphur content or that they want the maximum production regardless of the sulphur content. Each of these requires a different method of operating the furnace. The operator must also operate the furnace with the type of raw materials which are available'and furnished to him. Thus the quality of the coke may vary and the quality of the iron ore, sinter and/or pellets may vary. For the foregoing reasons it is impos sible to operate the furnace in such a manner that it will produce the maximum amount of best quality iron at all times.

I have found that there are four variables which are most important in considering the operation of the blast furnace. These are blast pressure, the condition of the gas leaving the top of the furnace, wind rate and moisture in the wind. The blast pressure and the top gas condition are variables which depend upon the type of burden in the furnace and the operating practice as it relates to the quality and quantity of iron produced. The top gas condition may be indicated by the percent of CO and/ or H2 content, by its temperature or by its B.t.u. content. I have found that there is an optimum blast pressure and optimum top gas condition combination for the operation of any blast furnace with any given burden and with any operating practice. When the blast pressure or top gas condition varies from the optimum, the furnace is not operating efficiently and is moving toward a troublesome unbalanced condition. I have also found that I can correct the furnace operation by controlling or varying the wind rate and the moisture content of the wind.

It is therefore an object of my invention to provide a method of operating a blast furnace which will consistently give better or optimum results for the type of burden which is furnished to the operator and the output which he has been ordered to obtain.

Another object is to provide such a method in which the blast pressure and the top gas condition are used as sensors and the wind rate and moisture content of the wind are varied to obtain the desired result.

Still another object is to provide such a method which corrects for random or permanent changes in the raw materials before the effect thereof is apparent to the operator.

Aatent 3,334,17l Patented Feb. 14, 1967 A further object is to provide such a method which will increase the coke eiliciency and utilize thewind more efiicently. v

A still further object is to provide such a method which results in smoother operation of the furnace, more efficient slag control and more uniform chemistry of the iron produced.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIGURE l is a schematic view of a blast furnace and its auxiliary equipment; and

FIGURE 2 is a chart utilized in the practice of the method of the invention.

Referring more particularly to the drawings reference numeral 2 indicates a blast furnace having the usual hearth 4, bosh 6, stack 8, large bell 10, small bell 12 and distributor 14. Raw materials including coke, limestone and iron ore are supplied to the top of the furnace through the usual skip hoist 16. The blast furnace gases pass from the top of the furnace and then down through a downcomer 18 to a dust catcher 2t). A bustle pipe 22 surrounds the blast furnace 2. Air is supplied to the bustle pipe 22 and hence to the tuyeres 24 through a hot blast line 26. A blower 28 feeds cold air through a cold blast line 30 to a stove 32 where it is heated before being delivered to the hot blast line 26. All of the equipment described is conventional. The blower 28 can be controlled to vary the amount of air delivered by means of a control 33 and means 34 are provided to measure and record the wind rate in standard cu. ft. per minute. A recording gage 35 is provided at the bustle pipe to measure the blast pressure in lbs. per sq. in. gage. Means 36 are provided to measure and record the moisture in grains per cu. ft. of air in the hot blast line 26. The amount of mois-ture in the air in the cold blast line 30 is varied by means of a steam jet 38. A temperature responsive device 4t) is provided in the downcomer 18 to measure and record the top temperature of the gas. A gas analyzer or Btu. meter may be used in place of the device 46, but the temperature responsive device is preferred because of its simplicity and hence the invention will hereinafter be described with the temperature reading as illustrative. It will be understood that the devices 32, 33, 34, 36, 3S and 4t) are all conventional and that the readings need not be taken at the exact positions indicated.

I have found that my method of control should be based upon the following cybernetic relationship or equation:

where X is the number of charges per hour, A is the volume of air or wind delivered in thousands of standard cu, ft. per minute, B is the total moisture in the blast in grains per cu. ft., C is the blast or bustle pressure in lbs. per sq. in. gage and D is the top temperature of the blast furnace gas in F. A charge is one complete filling sequence usually requiring two bell dumps into the furnace.

In order to carry out my invention I have developed the chart of FIGURE 2 based upon the above equation. Column 1 includes a slidable strip 42 on which is indicated actual bustle pressure in lbs. gage. Column 2 indicates the correction in wind volume in standard cu. ft. dependent upon actual bustle pressure. Column 3 indicates moisture correction in grains per cu. ft. based upon actual bustle pressure. Column 4 includes a slidable strip 44 on which is indicated actual top temperature in F. Column 5 indicates the wind volume correction in standard cu. ft. based upon actual top temperature. Column 6 indicates moisture correction in grains per cu. ft. based upon actual top temperature. Row 46 across all six columns may be termed the adjustable base row and Columns 2 and 3 have windows 48 and 50 in this base row. A slidable strip 52 having numbers thereon corresponding to total wind volume is slidably mounted below Column 2 and a similar slidable strip 54 having moisture content in grains per cu. ft. indicated thereon is slidably mounted below Column 3.

In carrying out my method I first determine the optimum or base values for wind volume, moisture, blast pressure and top temperature for the specific furnace to be controlled. This is accomplished through a zeroing in or initializing procedure which may be accomplished in various ways. The time required for this zeroing in procedure will vary depending upon how far the furnace process is out of balance. One suitable way of accomplishing this is -to (1) maintain the burden size charging sequence, stock line and blast temperature as constant as possible and to keep other changes through the furnace at the minimum permitted by the operation and production requirements. (2)- Stabilize the blast pressure by maintaining the wind volume against the burden at a sutlicient amount to cause the furnace to check once or twice between casts. More than two checks between casts indicates that too much wind is being blown and no check indicates that too little wind is being blown. (3) Stabilize the t-op -gas temperature at some mean level such as between 325 F. and 375 F. and stabilize moisture at some mean level such as 12 to 14 grains. If the top temperature is varying about a level higher than this, the moisture content should be increased until the desired level is reached. If the increased moisture begins to cool the hearth more than is desired for current operating requirements the amount of coke should beincreased. If the top temperature is Varying about a level below that desired the moisture should be reduced and if this results in the hearth heating up more than is desirable a decrease in coke is made. This operati-on is continued until the levels of 325 to 375 F. top temperature and 12 to 14 grains moisture is obtained. At this time the process is zeroed in and the average level of wind volume being blown is set in window 48 and the average moisture is set in window 50. This procedure results in a determination of the optimum blast pressure and the'optimum top temperature for the particular charge being used. The strips 42 and 44 are moved so that the optimum blast pressure and the optimum top temperature appear in row 4e.

At regular intervals the operator reads the blast pressure and top temperature recorder charts and estimates the average for the preceding time period. I have found that this period should not be less than three minutes since at least this length of time is required to make the necessary control changes and have the changes reiiected in the operation of the furnace. If automatic controls are used this minimum time interval can be used. However, in some instances, changes every six minutes may give best results and when the control is done manually longer periods may be necessary from practical considerations. In one particular instance, .satisfactory results have been obtained with manual operation and readings and adjustments made every half hour. In most cases periods longer than a half hour will be unsatisfactory, unless the charge materials are particularly uniform and of the best quality. If the actual blast pressure is higher than the optimum vthe wind rate is decreased and the moisture content increased. If the actual blast pressure is lower, then the optimum wind rate is increased and the moisture c-ontent decreased. If the top temperature is higher, then the optimum wind rate is decreased and the moisture content increased. If the top temperature isbelow the optimum the wind rate is increased and the moisture content decreased. In each of these cases the increases and decreases are directly proportional to the variance from the optimum. The amount of decrease in wind rate due to variance in blast ypressure is twice the amount of the increase for the same variance ,from the optimum blast pressure.

The amount of the decrease and increase in all other cases is the same for the same variance from the optimum. This is clearly shown in the chart of FIGURE 2.

Assuming for a particular furnace that the average moisture is 15 grains per cu. ft., the wind volume 76,000 cu. ft. per minute, the average or optimum bustle pressure 24 lbs. per sq. in., and the average or optimum top temperature 370 F. the strip 42 is moved until 24 appears in row 46 and strip 44 is moved until 370 appears in row 46. The strip 52 is moved until 76,000 appears in window 48 and strip 54 is moved until 15 appears in window 50. These last two indications are for convenience only. lf the bustle pressure is 24 lbs. per sq. in. and the top temperature 370 F. when a reading is taken no changes are necessary. When the next reading is taken the bustle pressure may be 25 lbs. per sq. in. and the top temperature 390 F. Referring to the chart of FIGURE 2 it will be seen that it is necessary to decrease the wind volume 500 cu. ft. per minute due to the increased bustle pressure and to decrease the wind volume 240 cu. ft. per min. because of the increase in top temperature. Thus the blower 23 will set to deliver 75,260 cu. ft. per minute. The moisture must be increased .75 grain per cu. ft. due to the higher bustle pressure and increased .4 grain per cu. ft. due to the higher top temperature. Thus additional moisture is added by the control 38 to obtain a moisture content of 16.15 grains per cu. ft. If, at the next reading, the pressure has decreased back to 24 lbs. per sq. in. and the temperature to 370 F. the moisture is reduced back to 15.0 grains per cu. ft. and the wind is reduced back to 76,000 cu. ft. per min. However, assuming that the bustle pressure has decreased to 23 lbs. and the top temperature to 350 F. the following changes are made: The wind volume must be increased 250 cu. ft. due to the lower blast pressure and 240 cu. ft. due to the lower temperature. The moisture must be reduced 0.75 grain due to the lower pressure and 0.4 grain due to the lower temperature. Thus the operator will set the blower to deliver 76,490 cu. ft. per min. and adjust the control 38 to give a moisture content of 13.85 grains per cu. ft. In actual practice with manual control the values of the wind volume and moisture content will be rounded of to amounts such as 75,300 cu. ft. instead of 75,260 and 16 grains instead of 16.15. Of course, with automatic control the corrections can be more precise. n f

When the analysis of the blast furnace gas or the Btu. content thereof are used in place of top gas temperature, the actual figures in Column 4 will be different than that shown, but the same proporitonal relationship will be present.

While one embodiment of my invention has been shown 1. The method of controlling the operation oa blastY furnace which comprises determining the optimum blast pressure and top gas condition for operation of the furnace with a given burden and operating practice, and controlling the wind rate and the moisture content thereof. to main the said optimum blast pressure and top gas condition: the wind rate being decreased a predetermined amount when the blast pressure is above the said optimum and increased a predetermined amount when the blast pressure is below the said optimum, said increase and decrease being directly proportional to the variance of said blast pressure from the said optimum with the amount of said decrease being twice the amount of said increase forV the same variance from the said optimum blast pressure; the moisture being increased a predetermined amount when the blast pressure is above the said optimum and decreased a predetermined amount when the blast pressure is below the said optimum, said increase and decrease being directly proportional to the variance of said blast pressure from the said optimum with the amount of said decrease and increase being the same for the same variance from the said optimum blast pressure; the wind rate being decreased a predetermined amount when the top gas condition is greater than the said optimum and increased a predetermined amount when the top gas condition is less than the said optimum, said increase and decrease being directly proportional to the variance of said top gas condition from the said optimum with the amount of said decrease and increase being the same for the same variance from the said optimum top gas condition; and the moisture being increased a predetermined amount when the top gas condition is greater than the said optimum and decreased a predetermined amount when the top gas condition is less than the said optimum, said increase and decrease being directly proportional to the variance of said top gas condition from the said optimum with the amount of said decrease and increase being the same for the same variance from the said optimum top gas condition.

2. The method yof controlling the operation of a blast furnace according to claim 1 in which the top gas con'dition is the temperature of the gas.

3. The method of controlling the operation of a blast furnace which comprises determining the optimum blast pressure and top gas condition for operation of the furnace with a given burden and operating practice, determining the actual blast pressure and top gas condition at intervals, decreasing the wind rate and increasing the moisture content of said wind when the determined blast pressure is higher than the said optimum, increasing the wind rate and decreasing the moisture content of said wind when the determined blast pressure is lower than the said optimum, decreasing the wind rate and increasing the moisture content of said wind when the determined top gas condition is greater than the said optimum, and increasing the wind rate and decreasing the moisture content of said wind when the determined t-op gas condition is less than said optimum.

4. The method of controlling the operation of a blast furnace according to claim 3 in which the increases and decreases are directly proportional to the variance of said blast pressure from the said optimum and directly proportional to the variance of said top gas condition from the said optimum, the amount of said decrease in wind rate due to variance in blast pressure is twice the amount of said increase for the same variance from the said optimum blast pressure, the amount of said decrease and increase in moisture content is the same for the same variance from the said optimum blast pressure, the amount of said increase and decrease in wind rate is the same for the same Variance from the said optimum top gas condition, and the amount of said increase and decrease in moisture content is the same for the same variance from the said optimum top gas condition.

5. The method of controlling the operation ofa blast furnace according to claim 3 in which the top gas condition is the temperature of the gas, the increases and decreases are directly proportional to the Variance of said blast pressure from the said optimum and directly proportional to the variance of said top gas temperature from the said optimum, the amount of said decrease in wind rate due to variance in blast pressure is twice the amount of said increase for the same variance from the said optimum blast pressure, the amount of said decrease and increase in moisture content is the same for the same Variance from the said optimum blast pressure, the amount of said increase and decrease in wind rate is the same for the same variance from the said optimum top gas temperature, and the amount of said increase and decrease in moisture content is the same for the same variance from the said optimum top gas temperature.

OTHER REFERENCES A.I.M.M.E. Blast Furnace, Coke Oven, and Raw Materials Committee Proceedings, volume 11, 1952, pages 24-28.

DAVID L. RECK, Primary Examz'ner.` 

3. THE METHOD OF CONTROLLING THE OPERATION OF A BLAST FURANCE WHICH COMPRISES DETERMINING THE OPTIMUM BLAST PRESSURE AND TOP GAS CONDITION FOR OPERATION OF THE FURNACE WITH A GIVEN BURDEN AND OPERATING PRACTICE, DETERMINING THE ACTUAL BLAST PRESSURE AND TOP GAS CONDITION AT INTERVALS, DECREASING THE WIND RATE AND INCREASING THE MOSITURE CONTENT OF SAID WIND WHEN THE DETERMINED BLAST PRESSURE IS HIGHER THAN THE SAID OPTIMUM, INCREASING THE WIND RATE AND DECREASING THE MOSITURE CONTENT OF SAID WIND WHEN THE DETERMINED BLAST PRESSURE IS LOWER THAN THE SAID OPTIMUM, DECREASING THE WIND RATE AND INCREASING THE MOISTURE CON- 